This invention relates generally to a device for reducing warpage of lumber during drying and cooling and, more particularly, to a leaf spring device that counteracts the drying stain during actual drying and cooling, thereby resulting in straighter dried lumber.
Lumber such as 2.times.4s, 2.times.6s, 2.times.8s, 2.times.10s and 2.times.12s are usually placed in a dry kiln after manufacture and taken down to a moisture content of about 15%. By reducing the moisture content of the lumber, it can then be used in many end-use applications without undergoing future deformation. Typically, lumber to be dried is uniformly stacked in a generally rectangular volume and is referred to as a load or charge. Lumber of a uniform thickness will be selected and stacked in horizontal rows between which are placed "stickers" that separate the rows. Oftentimes these loads of lumber to be dried will be stacked on bunks which are mounted on cars that can be rolled into a dry kiln. The upper layers in a load, unless there is some downward force exerted on the load, will be free to naturally bend upwardly during drying. The lower rows of lumber will, of course, have the weight of the upper rows atop them, thereby having a natural restraining force on them.
It has been recognized in the past that during drying when top rows of green lumber are free to deform they will in fact warp considerably. Such warpage, of course, reduces the market value and various means have been proposed to restrain such warpage. One device may be seen by referring to U.S. Pat. No. 1,212,583--Tanner wherein a restraining device is disclosed that utilizes a pair of beams placed across the load and held together by a spring device that continually exerts a restraining force on the entire load of lumber. It is also known that a static load can be placed on the load such as concrete blocks to restrain warping.
With today's dry kilns, restraining devices are useful but they must be designed so as to fit within the confines of the kiln and in view of the kiln baffling system. The restraining device should not impair the functioning of the baffling system. The device must also be reasonably inexpensive and must serve to exert the continuing restraining force as the load shrinks in size.
Accordingly, from the foregoing, one object of the present invention is to minimize the warpage of lumber during drying and cooling. Another object of this invention is to provide such a device that is relatively inexpensive and easy to manufacture. Yet a further object of this invention is to provide a restraining device that is readily usable with today's dry kilns with their internal baffling systems. These and other objects of the present invention will be more fully understood by reading the following specification in conjunction with the attached drawings.